Plant Reproduction and Biotechnology Chapter 38

I) Sexual Reproduction A) Alternation of Generation 1) haploid(n) and diploid(2n) generations take turns producing each other

2) Angiosperms and gymnosperms a) sporophyte generation is the most visible, with the flower/cones creating the gametophyte

B) Flowers 1) (know all the structures) 2) bisexual flower: has both male and female 3) unisex has male or female

4) monoecious: a plant that has both male and female flowers 5) dioecious: one plant has only male or female flowers

C) Male gametophytes 1) Sporangia(pollen sacs) have microsporocytes(2n) 2) This divides by meiosis to create 4 microspores(n)

3) microspore divides by mitosis to create a generative cell and a tube cell 4) these are protected by a hard outer shell = pollen grain

5) when pollen lands on stigma generative cell divides by mitosis to create 2 sperm cells. It is now a mature male gametophyte

D) Female gametophyte(embryo sac) 1)Ovule has a sporangium with a megasporocyte inside 2) megasporocyte goes through meiosis to make 1 large megaspore and 3 small cells that die

3) megaspore divides by mitosis to make: 3 antipodal cells 2 polar nuclei 1 egg 2 synergids

E)Pollination 1) pollen lands on stigma. 2) pollen tubes extends towards ovary 3) Double fertilization: 1 sperm fertilizes ovule and 1 fuses with polar nuclei a) this makes 3n endosperm(feeds developing seed)

F) Control of pollination 1) want to avoid self pollination a) anther and stigma develop at different times b) physical shape prevents this

c) self-incompatibility c1) stigma can tell if genes are same or are too close and blocks pollen tube from forming

G) Seed formation 1) ovule turns into the seed a) endosperm begins as a liquid, then solidifies when cell walls are added

2) structure of a seed a) seed coat: protects seed b) hypocotyl: c) radicle: extends to form root d) epicotyl: extends to form stem

3) fruit a) job is to disperse seed a1) apples, tomatoes, etc. are energy/nutrient rich to entice animals to eat them.

a2) some fruit is adapted for other types of dispersal a2) some fruit is adapted for other types of dispersal * grains are actually a fruit tightly bound to the seed coat

H) Adaptations for seed survival 1) Dormancy: seed dehydrates and lowers metabolic rate.

2) waiting for conditions appropriate for growth a) moisture b) warmth c) some need chemical attack from digestion

3) germination a) imbibition: water uptake by dry seed ruptures seed coat a1) radicle emerges and grows down

a2) hypocotyl form a hook, so as the shoot grows it pulls the cotyledons(and epicotyl) out of ground, protecting the apical meristem

b) some plants germinate differently b1) peas b2) corn

II) Asexual reproduction A) Plant cloning(vegetative reproduction) 1) fragmentation: part of a plant falls off, adventitious roots form, and start a new plant.

2) shoots can also form from roots and create a new plant.

3) apomixis: diploid cell in ovule creates a seed and is then dispersed a) dandelion can do this

B) Use of Cloning in Agriculture 1) most commercial plants are cuttings a) most plants need a stem, and having a node helps a1) some plants just need a leaf

2) Trees a) stock: plant that proved roots b) scion: part from another tree grafted on to stock

C) Transgenic (genetically modified) plants 1) crossbreeding by farmers create plants with desirable traits a) new corn with hard endosperm and high levels of lysine and tryptophan

2) genes can now be added to plants to give them traits 2) genes can now be added to plants to give them traits. a) create own pesticides b) create own herbicides

3) debate against transgenic plants: a) transfer of allergens b) creation of “superbugs” resistant to plant pesticides

c) transfer of genes to wild plants c) transfer of genes to wild plants. d) adverse effect on non-target species d1) monarch larvae dying when eating pollen from corn that landed on milkweed